Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing the new design.

FIG. 2 is another front view thereof, but with an alternate broken line disclosure; and,

FIG. 3 is another front view thereof, but with an alternate broken line disclosure.

Within the drawings, the broken lines illustrate the display screen or portion thereof and portions of the graphical user interface. None of the broken lines form part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 